Disclosed generally is a practical system of measuring road surface friction using an auxiliary wheel and more particularly to a system wherein a switch in the cab deploys the measuring wheel and the in-cab display gives a continuous reading of road surface friction as soon as the wheel rotates. The road friction tester (“RFT”) is designed for use in the trucking industry to determine road surface grip where driving conditions may be hazardous.
In U.S. Pat. No. 6,840,098 (the “'098 patent”, which is incorporated herein by reference) the original GEM™ device is disclosed to include a vehicle and a device for measuring road surface friction, which device is affixed to the vehicle. The device for measuring road surface friction includes an auxiliary wheel mounted to the vehicle and between the vehicle and the road surface. The auxiliary wheel is toed in or toed out, loaded, and mounted on an axle for its free rolling. A calibrated force sensor is associated with the auxiliary wheel to measure the isolated axial force thereon. A converter displays the road friction and displays it to the vehicle operator or remotely. The GEM™ device is used for measuring road surface friction of a road surface and uses a vehicle that moves across the road surface. An auxiliary independent wheel is interposed between the vehicle and the road surface. The auxiliary wheel is freely rotatable by movement of the vehicle and is toed in or toed out (skewed) with respect to a direction of travel of the vehicle so as to create an axial force on the auxiliary wheel. The axial force on the auxiliary wheel is isolated and measured while the vehicle moves across the road surface. The measured axial force is correlated with the road surface friction.
While such design has been determined to work effectively and efficiently when used in conjunction with a snow plow or other heavy vehicle, a modified design was determined to be needed when the GEM™ device was towed behind or mounted under a small vehicle, such as a SUV, pickup truck, or like light-weight vehicle, such as a passenger vehicle or car.
It is to such lightweight vehicle RFT device (the RT3™ device) that the present invention is based.
Broad Statement
A method for measuring road surface friction of a road surface uses a vehicle that moves across the road surface wherein (1) an auxiliary independent wheel assembly is towed behind the vehicle and is in contact with the road surface, an auxiliary wheel of the wheel assembly is freely rotatable by movement of the vehicle and is one or more of toed in or toed out with respect to a direction of travel of the vehicle so as to create an isolated axial force on the auxiliary wheel: (2) the axial force on the auxiliary wheel is measured while the vehicle moves across the road surface, and the measured axial force is correlated with the road surface friction. The independent wheel assembly is load isolated from the weight of the towing vehicle and the independent wheel assembly is loaded by placing ballast thereon. A variety of improvements are disclosed which have particular relevance when a normal passenger vehicle (car, light duty truck, or SUV) is used to tow the RGT.
These drawings will be described in further detail below.